1. Technical Field
The present application relates to a plasma display panel (PDP). More particularly, the present application relates to a PDP with enhanced luminescence efficiency at a reduced discharge firing voltage.
2. Discussion Of Related Technologies
A three-electrode surface-discharge type plasma display panel (PDP) is an example of a common type of PDP. The three-electrode surface-discharge type PDP includes a front substrate and a rear substrate, and a discharge gas filling the space formed therebetween.
Parallel sets of elongated sustain electrodes and scan electrodes are provided on the interior surface of the front substrate. Elongated address electrodes are provided on the rear substrate, which is spaced apart from the front substrate. The address electrodes extend in a direction that intersects the direction of (i.e., not parallel with) the sustain electrodes and scan electrodes. Discharge cells are formed between the front and rear substrates, each of which is associated with a sustain electrode, a scan electrode, and an address electrode.
In a three-electrode surface-discharge type PDP, a discharge cell is selected by an address discharge between the sustain and address electrodes, which are controlled independently. In addition, a glow discharge is generated in the selected discharge cell by a sustain discharge between the sustain and scan electrodes disposed on the interior of the front substrate.
Visible light is generated from the glow discharge in a multistep process. In a glow discharge, collisions between electrons and discharge gas molecules generate vacuum ultraviolet (VUV) radiation. Absorbing VUV radiation causes a phosphor layer in the discharge cell to fluoresce, thereby generating visible light. An observer views the visible light through a transparent front substrate.
Typically, power losses at various stages of the discharge process described above result in a substantial overall power loss. For example, the glow discharge is triggered by applying a voltage higher than a discharge firing voltage between the sustain electrode and the scan electrode. That is, a very high voltage is required to trigger the glow discharge. Once a glow discharge is triggered, the voltage distribution between the cathode and the anode of a discharge cell is distorted by a space charge effect formed at a dielectric layer near the cathode and the anode. In particular, a cathode sheath region, an anode sheath region, and a positive column region form between the electrodes. The cathode sheath region forms near the cathode and consumes a majority of the voltage applied to the electrodes. The anode sheath region forms near the anode and consumes only a part of the applied voltage. The positive column region forms between the two sheath regions and consumes a negligible amount of the applied voltage.
A portion of the power dissipated at these regions heats the electrons in the discharge cell. The efficiency of the electron heating is referred to herein as the “electron heating efficiency.” The electron heating efficiency of the cathode sheath region depends on a secondary electron emission coefficient of a protective layer, typically, a MgO layer, formed over the scan and sustain electrodes. The electron heating efficiency of the positive column region is typically high.
As discussed above, collisions between a discharge gas, for example, xenon gas, and electrons generate excited state xenon atoms. Relaxation of the excited state xenon atoms back to the ground state generates vacuum ultraviolet (VUV) radiation. Consequently, a method for increasing the luminescence efficiency (i.e., a ratio of the visible light to the input power) of a PDP is to increase the collisions between the electrons and the xenon gas. Increasing the electron heating efficiency increases the number and energy of collisions between the electrons and the xenon gas, thereby increasing the luminescence efficiency.
As discussed above, most of the input power is consumed in the cathode sheath region; however, the electron heating efficiency is low in that region. By contrast, the positive column region consumes only a small portion of the input power, but the electron heating efficiency is very high. Accordingly, increasing the size of the positive column region, for example, by increasing a discharge gap between the electrodes, increases the luminescence efficiency.
The luminescence efficiency also increases in a discharge gas comprising xenon and neon as a partial pressure of xenon increases. Electron consumption ratios (the ratio of consumed electrons to all electrons) for xenon excitation (Xe*), xenon ionization (Xe+), neon excitation (Ne*), and neon ionization (Ne+) depend on a reduced electric field (the ratio E/n, where, E is the electric field at the discharge gap and n is gas density). For a given value of reduced electric field (E/n), the electron energy decreases as the partial pressure of xenon increases. As the electron energy decreases, the electron consumption ratio for the xenon excitation increases. Because VUV radiation is generated by the relaxation of xenon from an excited state to the ground state, the luminescence efficiency also increases as the electron consumption ratio for the xenon excitation increases.
As discussed above, both increasing the size of the positive column region, and increasing the partial pressure of xenon in the discharge gas increase the electron heating efficiency in xenon excitation (Xe*). Therefore, either or both of these features can be used for increasing the electron heating efficiency, thereby improving the luminescence efficiency. Increasing either or both the positive column region and/or the partial pressure of xenon typically requires an increased discharge firing voltage, which also increases the manufacturing cost of a PDP, however. Consequently, it is would be desirable to keep the discharge firing voltage at a low level while simultaneously improving the luminescence efficiency by increasing the size of the positive column region and/or the partial pressure of xenon in the discharge gas. For a given discharge gap and gas pressure, the discharge firing voltage is generally lower in an opposed discharge configuration, in which scan and sustain electrodes face each other, than in a surface discharge configuration described above.
The disclosure in this Background section is provided only to aid the reader in understanding of the background of the invention and may contain information not be known to a person of ordinary skill in the art. Accordingly, the information disclosed in the Background section is not admitted to be prior art.